PROJECT SUMMARY The transcription factor NF-?B is responsible for inducing the expression of a plethora of genes that are essential for immune function. The signaling pathways that activate the NF-?B system have been extensively studied and require the degradation of inhibitory factors known as ?classical? I?B proteins (I?B-?, -?, and -?). In addition, work supported by this grant uncovered that degradation of NF-?B subunits plays an essential part in terminating pro-inflammatory gene expression. These degradation events are dependent on specific members of the COMMD protein family: COMMD1 is needed for optimal degradation of NF-?B/RelA, and in a similar fashion, optimal degradation of I?B is dependent on COMMD8. In more recent work, we discovered that COMMD proteins are integral components of a regulatory complex that controls endosomal protein sorting: the COMMD/CCDC22/CCDC93 or CCC complex. A variety of proteins that traverse endosomes depend on this complex to be trafficked properly to their final destination. Preliminary data now demonstrate that in myeloid cells, COMMD proteins not only regulate NF-?B signaling, but also play an intrinsic role in phagocytosis. In vivo, inactivation of this system in myeloid cells leads to increased bacterial penetration in the colonic mucosa, which promotes colon adenoma formation in genetically susceptible mice. Based on these observations, we hypothesize that the CCC complex regulates key aspects of myeloid cell immune function, including NF-?B signaling, phagocytosis, and the roles of these cells during tumor development. The overall goal of this project is to examine the role of the CCC complex in immune function at three levels of increasing system complexity through these specific aims: (1) To evaluate the role of endosomes in NF-?B signaling: Our data indicate that loss of CCC complex subunits leads to disruption in I?B degradation. In this aim we will evaluate the hypothesis that the CCC complex is responsible for ?organizing? I?B turnover on endosomal membrane surfaces. (2) To examine the mechanism by which the CCC complex regulates the phagocytic process: Preliminary studies indicate that the CCC complex localizes to phagolysosomes and we find that Commd1 deletion in myeloid cells impairs the phagocytic elimination of bacteria. In this aim we will systematically assess potential mechanisms by which the CCC complex might assist the phagocytic process. (3) To examine the role of the CCC complex in intestinal immunity and cancer progression: Preliminary studies in the myeloid-specific Commd1 knockout mice identified greater penetration of commensal bacteria into the lamina propria of the colon. Unexpectedly, colon adenoma formation is greatly enhanced in genetically susceptible mice (ApcMin mice) upon deletion of Commd1 in myeloid cells and this is dependent on intestinal bacteria. In this Aim we will test the hypothesis that microbial elimination by myeloid cells in the intestinal lamina propria can affect tumor development. Altogether, this proposal is intended to provide insights that have the potential of shifting our current understanding of critical pathways in immune function and human disease.